C-ML TODO and Future Implementations
This document lists planned features, improvements, and enhancements for the C-ML library.
Table of Contents
High Priority
1. Additional Neural Network Layers
Conv1d - 1D Convolution
- Status: Not implemented
- Priority: High
- File:
src/nn/layers/conv1d.c,include/nn/layers/conv1d.h - Description: 1D convolution for time series data, audio processing, and sequence models
- Implementation Notes:
- Similar to Conv2d but operates on 1D tensors
- Input shape:
[batch, in_channels, length] - Output shape:
[batch, out_channels, out_length] - Support stride, padding, dilation
- Use direct convolution loops (similar to Conv2d implementation)
- Related Files:
src/nn/layers/conv2d.c(reference implementation) - Benefits: Essential for time series models, RNNs, and audio processing
Conv3d - 3D Convolution
- Status: Not implemented
- Priority: High
- File:
src/nn/layers/conv3d.c,include/nn/layers/conv3d.h - Description: 3D convolution for video processing, medical imaging, and volumetric data
- Implementation Notes:
- Extends Conv2d to 3D spatial dimensions
- Input shape:
[batch, in_channels, depth, height, width] - Output shape:
[batch, out_channels, out_depth, out_height, out_width] - Support stride, padding, dilation in all 3 dimensions
- Related Files:
src/nn/layers/conv2d.c(reference implementation) - Benefits: Required for video analysis, 3D medical imaging, and volumetric CNNs
LayerNorm - Layer Normalization
- Status: ✅ IMPLEMENTED
- Priority: High
- File:
src/nn/layers/layernorm.c,include/nn/layers/layernorm.h - Description: Layer normalization for transformer architectures and modern NLP models
- Implementation:
- Normalizes across features (last dimension)
- Formula:
(x - mean) / sqrt(var + eps) * gamma + beta - Similar to BatchNorm2d but normalizes across different dimensions
- No running statistics needed (stateless normalization)
- Learnable parameters:
gamma(scale) andbeta(shift) - Benefits: Essential for transformers, BERT, GPT models, and modern NLP architectures
GroupNorm - Group Normalization
- Status: Not implemented
- Priority: Medium-High
- File:
src/nn/layers/groupnorm.c,include/nn/layers/groupnorm.h - Description: Group normalization alternative to BatchNorm, useful for small batch sizes
- Implementation Notes:
- Divides channels into groups and normalizes within each group
- Works well with batch size 1 (unlike BatchNorm)
- Formula similar to BatchNorm but groups channels
- Learnable parameters:
gammaandbetaper group - Related Files:
src/nn/layers/batchnorm2d.c(reference implementation) - Benefits: Better than BatchNorm for small batches, used in modern architectures
ModuleList - Dynamic Module List
- Status: Not implemented
- Priority: Medium-High
- File:
src/nn/layers/modulelist.c,include/nn/layers/modulelist.h - Description: Container for dynamically adding/removing modules
- Implementation Notes:
- Similar to Sequential but allows indexing and modification
- Maintains array of Module pointers
- Supports
append(),insert(),remove(),get() - Collects parameters from all submodules
- Related Files:
src/nn/layers/sequential.c(reference implementation) - Benefits: Flexible model construction, dynamic architectures
ModuleDict - Named Module Dictionary
- Status: Not implemented
- Priority: Medium-High
- File:
src/nn/layers/moduledict.c,include/nn/layers/moduledict.h - Description: Container for named modules (key-value pairs)
- Implementation Notes:
- Hash table or array of (name, Module*) pairs
- Supports
add(),get(),remove(),keys() - Collects parameters from all submodules
- Related Files:
src/nn/layers/sequential.c(reference implementation) - Benefits: Named access to modules, better organization
2. Optimizer Improvements
SGD Momentum Buffer
- Status: TODO in code (line 339 in
src/optim.c) - Priority: High
- File:
src/optim.c,include/optim/optimizer.h - Description: Implement proper momentum buffer for SGD optimizer
- Current Implementation: Simple SGD without momentum buffer
- Implementation Notes:
// Current (line 339): // TODO: Implement momentum buffer // For now, simple SGD without momentum buffer // Need to: // 1. Store velocity buffer per parameter // 2. Update: v = momentum * v - lr * grad // 3. Update: param = param + v - Benefits: Faster convergence, smoother optimization
RMSprop Optimizer
- Status: IMPLEMENTED
- Priority: High
- File:
src/optim.c,include/optim/optimizer.h - Description: Root Mean Square Propagation optimizer
- Implementation:
- Added
RMSpropStatestructure withsquare_avgtensor - Update rule:
square_avg = alpha * square_avg + (1 - alpha) * grad^2 - Parameter update:
param = param - lr * grad / sqrt(square_avg + eps) - Parameters:
lr,alpha(decay rate, default 0.99),eps(numerical stability) - Proper state initialization and cleanup
- Function:
optim_rmsprop(parameters, num_parameters, lr, weight_decay, alpha, epsilon) - Benefits: Good for non-stationary objectives, alternative to Adam
Adagrad Optimizer
- Status: IMPLEMENTED
- Priority: High
- File:
src/optim.c,include/optim/optimizer.h - Description: Adaptive Gradient optimizer with per-parameter learning rates
- Implementation:
- Added
AdagradStatestructure withsum_sq_gradtensor - Accumulates squared gradients:
sum_sq_grad += grad^2 - Update:
param = param - lr * grad / sqrt(sum_sq_grad + eps) - No momentum, adaptive learning rates
- Proper state initialization and cleanup
- Function:
optim_adagrad(parameters, num_parameters, lr, weight_decay, epsilon) - Benefits: Automatic learning rate adaptation, good for sparse gradients
AdamW Optimizer
- Status: Not implemented
- Priority: High
- File:
src/optim.c,include/optim/optimizer.h - Description: Adam with decoupled weight decay (fixes weight decay in Adam)
- Implementation Notes:
- Similar to Adam but weight decay is applied separately
- Update:
param = param - lr * (m_hat / sqrt(v_hat) + weight_decay * param) - Better than Adam for regularization
- Related Files:
src/optim.c(Adam implementation as reference) - Benefits: Better generalization than Adam, preferred in modern training
AdaDelta Optimizer
- Status: Not implemented
- Priority: Medium
- File:
src/optim.c,include/optim/optimizer.h - Description: Adaptive learning rate optimizer without manual learning rate
- Implementation Notes:
- Maintains moving averages of gradients and parameter updates
- No learning rate parameter needed
- Update uses accumulated updates instead of learning rate
- Benefits: No need to tune learning rate, adaptive
Learning Rate Schedulers
- Status: Not implemented
- Priority: High
- File:
src/optim/lr_scheduler.c,include/optim/lr_scheduler.h - Description: Various learning rate scheduling strategies
- Schedulers to Implement:
- StepLR: Decay by factor every N epochs
- ExponentialLR: Exponential decay:
lr = lr * gamma^epoch - CosineAnnealingLR: Cosine annealing schedule
- ReduceLROnPlateau: Reduce LR when metric plateaus
- MultiStepLR: Decay at specific milestones
- OneCycleLR: One cycle policy (popularized by fastai)
- Implementation Notes:
- Create scheduler interface that takes optimizer
- Call
scheduler_step()after each epoch or batch - Update optimizer learning rates
- Benefits: Better convergence, automatic learning rate tuning
3. Loss Functions
KL Divergence Loss
- Status: ✅ IMPLEMENTED
- Priority: High
- File:
src/autograd/loss_functions.c,include/autograd/loss_functions.h - Description: Kullback-Leibler divergence for probability distributions
- Formula:
KL(P||Q) = sum(P * log(P / Q)) - Use Cases: Variational autoencoders, knowledge distillation, regularization
- Implementation: Forward pass computes KL divergence, backward computes gradients
Hinge Loss
- Status: Not implemented
- Priority: Medium
- File:
src/autograd/loss_functions.c,include/autograd/loss_functions.h - Description: Maximum margin classifier loss
- Formula:
max(0, 1 - target * output) - Use Cases: Support vector machines, binary classification
- Implementation: Element-wise max operation with backward pass
Huber Loss
- Status: ✅ IMPLEMENTED
- Priority: Medium
- File:
src/autograd/loss_functions.c,include/autograd/loss_functions.h - Description: Robust loss function, less sensitive to outliers than MSE
- Formula:
- If
|x| < delta:0.5 * x^2 - Else:
delta * |x| - 0.5 * delta^2 - Use Cases: Robust regression, outlier handling
- Parameters:
delta(threshold parameter)
Focal Loss
- Status: Not implemented
- Priority: Medium
- File:
src/autograd/loss_functions.c,include/autograd/loss_functions.h - Description: Addresses class imbalance in classification
- Formula:
-alpha * (1 - p)^gamma * log(p) - Use Cases: Object detection, imbalanced datasets
- Parameters:
alpha(weighting factor),gamma(focusing parameter)
Smooth L1 Loss
- Status: Not implemented
- Priority: Medium
- File:
src/autograd/loss_functions.c,include/autograd/loss_functions.h - Description: Smooth version of L1 loss, used in object detection
- Formula:
- If
|x| < beta:0.5 * x^2 / beta - Else:
|x| - 0.5 * beta - Use Cases: Faster R-CNN, object detection
- Related: Similar to Huber loss but different parameterization
4. Backward Pass Verification
Complete Backward Pass Audit
- Status: Needs verification
- Priority: High
- Files:
src/autograd/forward_ops.c,src/autograd/backward_ops.c - Description: Verify all forward operations have corresponding backward passes
- Tasks:
- List all operations in
forward_ops.c - Check if each has a backward function in
backward_ops.c - Verify gradient correctness
- Test backward passes with numerical gradients
- Operations to Check:
- All binary operations (add, sub, mul, div, pow)
- All unary operations (exp, log, sqrt, sin, cos, tan)
- All activation functions (relu, sigmoid, tanh)
- All reduction operations (sum, mean, max, min)
- Matrix operations (matmul, transpose)
- Loss functions (mse, mae, bce, cross_entropy)
- Benefits: Ensure all operations support training
5. Model Persistence
Model Saving and Loading
- Status: Not implemented
- Priority: High
- File:
src/nn/model_io.c,include/nn/model_io.h - Description: Save and load model weights and architectures
- Features to Implement:
- Save Model State: Save all parameters to file
int model_save(Module *model, const char *filepath); - Load Model State: Load parameters from file
int model_load(Module *model, const char *filepath); - Save Full Model: Save architecture + parameters
int model_save_full(Module *model, const char *filepath); - Load Full Model: Reconstruct model from saved file
Module *model_load_full(const char *filepath); - Checkpoint Support: Save checkpoints during training
int model_save_checkpoint(Module *model, Optimizer *optimizer, int epoch, float loss, const char *filepath); - Resume Training: Load checkpoint and continue training
int model_load_checkpoint(Module *model, Optimizer *optimizer, int *epoch, float *loss, const char *filepath); - File Format: JSON or binary format for parameters
- Benefits: Model persistence, checkpointing, model sharing
Medium Priority
6. Activation Functions
ELU (Exponential Linear Unit)
- Status: Not implemented
- Priority: Medium
- File:
src/nn/layers/activations.c,include/nn/layers/activations.h - Description: ELU activation function with smooth negative values
- Formula:
x if x > 0 else alpha * (exp(x) - 1) - Implementation: Similar to ReLU but with exponential for negative values
- Benefits: Better than ReLU for negative inputs, prevents dead neurons
SELU (Scaled Exponential Linear Unit)
- Status: Not implemented
- Priority: Medium
- File:
src/nn/layers/activations.c,include/nn/layers/activations.h - Description: Self-normalizing activation function
- Formula:
lambda * (x if x > 0 else alpha * (exp(x) - 1)) - Parameters:
lambda = 1.0507,alpha = 1.6733(fixed values) - Benefits: Self-normalizing networks, no need for BatchNorm
Swish/SiLU (Sigmoid Linear Unit)
- Status: Not implemented
- Priority: Medium
- File:
src/nn/layers/activations.c,include/nn/layers/activations.h - Description: Smooth, non-monotonic activation
- Formula:
x * sigmoid(x) - Implementation: Use existing sigmoid implementation
- Benefits: Better performance than ReLU in many cases
Mish
- Status: Not implemented
- Priority: Medium
- File:
src/nn/layers/activations.c,include/nn/layers/activations.h - Description: Self-regularized activation function
- Formula:
x * tanh(softplus(x))wheresoftplus(x) = log(1 + exp(x)) - Benefits: Smooth, non-monotonic, better than Swish in some cases
Hard Swish
- Status: Not implemented
- Priority: Medium
- File:
src/nn/layers/activations.c,include/nn/layers/activations.h - Description: Hard version of Swish, faster computation
- Formula:
x * relu6(x + 3) / 6whererelu6(x) = min(max(x, 0), 6) - Benefits: Faster than Swish, used in mobile architectures
7. Data Loading Improvements
Multi-threaded Data Loading
- Status: Not implemented
- Priority: Medium
- File:
src/Core/dataset.c,include/Core/dataset.h - Description: Parallel data loading using threads
- Implementation Notes:
- Use pthreads or similar threading library
- Prefetch batches in background threads
- Queue system for loading batches ahead of time
- Benefits: Faster training, better GPU utilization
Data Augmentation Utilities
- Status: Not implemented
- Priority: Medium
- File:
src/Core/data_augmentation.c,include/Core/data_augmentation.h - Description: Image and data augmentation functions
- Augmentations to Implement:
- Random crop, random flip (horizontal/vertical)
- Random rotation, random brightness/contrast
- Color jitter, normalization
- Mixup, CutMix (advanced augmentations)
- Benefits: Better generalization, data efficiency
Better Batch Sampling
- Status: Basic implementation exists
- Priority: Medium
- File:
src/Core/dataset.c - Improvements:
- Weighted sampling
- Stratified sampling
- Random sampling with seed control
- Sequential sampling
- Benefits: Better training dynamics
Prefetching
- Status: Not implemented
- Priority: Medium
- File:
src/Core/dataset.c - Description: Preload next batch while current batch is being processed
- Implementation: Background thread or async loading
- Benefits: Eliminate data loading bottlenecks
8. Tensor Operations
Concatenate
- Status: Not implemented
- Priority: Medium
- File:
src/tensor/ops.c,include/tensor/ops.h - Description: Concatenate tensors along specified dimension
- Function:
Tensor *tensor_concat(Tensor **tensors, int num_tensors, int dim) - Use Cases: Combining feature maps, joining layers
Stack
- Status: Not implemented
- Priority: Medium
- File:
src/tensor/ops.c,include/tensor/ops.h - Description: Stack tensors along new dimension
- Function:
Tensor *tensor_stack(Tensor **tensors, int num_tensors, int dim) - Use Cases: Batch creation, stacking outputs
Split
- Status: Not implemented
- Priority: Medium
- File:
src/tensor/ops.c,include/tensor/ops.h - Description: Split tensor into multiple tensors along dimension
- Function:
Tensor **tensor_split(Tensor *tensor, int num_splits, int dim) - Use Cases: Unpacking, splitting outputs
Gather
- Status: Not implemented
- Priority: Medium
- File:
src/tensor/ops.c,include/tensor/ops.h - Description: Gather values from tensor using indices
- Function:
Tensor *tensor_gather(Tensor *input, Tensor *indices, int dim) - Use Cases: Indexing, embedding lookups
Scatter
- Status: Not implemented
- Priority: Medium
- File:
src/tensor/ops.c,include/tensor/ops.h - Description: Scatter values into tensor at specified indices
- Function:
Tensor *tensor_scatter(Tensor *input, Tensor *indices, Tensor *src, int dim) - Use Cases: Sparse updates, embedding updates
Advanced Reductions
- Status: Not implemented
- Priority: Medium
- File:
src/tensor/ops.c,include/tensor/ops.h - Operations:
- Standard Deviation:
Tensor *tensor_std(Tensor *tensor, int dim, bool unbiased) - Variance:
Tensor *tensor_var(Tensor *tensor, int dim, bool unbiased) - Argmax:
Tensor *tensor_argmax(Tensor *tensor, int dim) - Argmin:
Tensor *tensor_argmin(Tensor *tensor, int dim) - Use Cases: Statistics, finding max/min indices
9. Memory Management
Memory Pool Allocator
- Status: Not implemented
- Priority: Medium
- File:
src/Core/memory_management.c,include/Core/memory_management.h - Description: Pre-allocated memory pools for tensor operations
- Benefits: Faster allocations, reduced fragmentation, better cache locality
Tensor Reuse
- Status: Partial support
- Priority: Medium
- File:
src/tensor/tensor.c - Description: Reuse tensor memory for intermediate computations
- Implementation: Tensor pool for common sizes
- Benefits: Reduced memory allocations, better performance
Gradient Checkpointing
- Status: Not implemented
- Priority: Medium
- File:
src/autograd/autograd.c,include/autograd/autograd.h - Description: Trade computation for memory in backward pass
- Implementation: Recompute activations during backward instead of storing
- Benefits: Enable training of larger models with limited memory
Memory Profiling
- Status: Not implemented
- Priority: Medium
- File:
src/Core/memory_management.c - Description: Track memory usage, identify leaks, profile allocations
- Features: Memory usage statistics, leak detection, allocation tracking
- Benefits: Better debugging, memory optimization
10. Broadcasting
Complete NumPy-style Broadcasting
- Status: Limited support
- Priority: Medium
- Files:
src/tensor/ops.c,src/autograd/backward_ops.c - Description: Full broadcasting support for all operations
- Current Limitations:
- Some operations may not handle broadcasting correctly
- Backward passes may not handle broadcasting gradients
- Implementation Tasks:
- Broadcast shapes before operations
- Handle gradient broadcasting in backward passes
- Support broadcasting for all binary operations
- Add broadcasting tests
- Broadcasting Rules:
- Align dimensions from right
- Dimensions must be equal or one of them is 1
- Missing dimensions are treated as 1
- Benefits: More flexible operations, NumPy compatibility
Low Priority
11. GPU Support
CUDA Implementation
- Status: Not implemented
- Priority: Low (but high impact)
- Files:
src/cuda/(new directory) - Description: GPU acceleration using CUDA
- Components:
- CUDA tensor operations
- GPU-accelerated autograd
- Memory management for GPU
- CUDA kernels for common operations
- Benefits: Significant speedup for large models
OpenCL Support
- Status: Not implemented
- Priority: Low
- Description: Cross-platform GPU support
- Benefits: Works on AMD, Intel, and other GPUs
12. Advanced Features
JIT Compilation
- Status: Not implemented
- Priority: Low
- Description: Just-In-Time compilation for operations
- Benefits: Faster execution for repeated operations
Parallel Backward Pass
- Status: Not implemented
- Priority: Low
- Description: Parallel execution of backward operations
- Benefits: Faster backward pass for large models
Double Backward (Grad of Grad)
- Status: Basic support exists
- Priority: Low
- Description: Complete support for higher-order derivatives
- Benefits: Advanced optimization techniques, meta-learning
Performance Optimizations
13. Operation Optimizations
SIMD Optimizations
- Status: Not implemented
- Priority: Medium-High
- Files:
src/tensor/ops.c - Description: Use SIMD instructions for element-wise operations
- Operations: Add, Mul, ReLU, Sigmoid, Tanh, etc.
- Benefits: 2-4x speedup for element-wise operations
BLAS Integration
- Status: Not implemented
- Priority: Medium
- Files:
src/tensor/ops.c - Description: Use optimized BLAS libraries for matrix operations
- Operations: Matrix multiplication, dot product
- Libraries: OpenBLAS, Intel MKL, ATLAS
- Benefits: Significantly faster matrix operations
im2col for Convolutions
- Status: Not implemented
- Priority: Medium
- File:
src/nn/layers/conv2d.c - Description: Use im2col transformation for faster convolutions
- Benefits: Faster convolutions, especially for large kernels
14. Memory Optimizations
In-Place Operations
- Status: Partial support
- Priority: Medium
- Description: Expand in-place operation support for memory efficiency
- Operations: Add, Mul, ReLU (in-place versions)
- Benefits: Reduced memory usage
Testing and Quality
15. Unit Tests
Comprehensive Test Suite
- Status: Basic tests may exist
- Priority: High
- Files:
test/directory - Coverage Needed:
- Tensor operations (all operations)
- Autograd operations (forward and backward)
- Neural network layers (all layers)
- Optimizers (SGD, Adam, and future optimizers)
- Loss functions (all loss functions)
- Testing Framework: Create or use existing C testing framework
- Benefits: Ensure correctness, prevent regressions
Integration Tests
- Status: Not implemented
- Priority: Medium
- Description: End-to-end training tests
- Tests:
- Complete training loop
- Model checkpointing and resuming
- Parameter saving and loading
- Benefits: Verify system integration
16. Code Quality
Static Analysis
- Status: Partial
- Priority: Medium
- Tools: cppcheck, clang-tidy, clang-analyzer, PVS-Studio
- Benefits: Catch bugs early, improve code quality
Code Coverage
- Status: Not implemented
- Priority: Medium
- Description: Measure and improve test coverage
- Tools: gcov, lcov
- Goal: 80%+ coverage for critical paths
- Benefits: Identify untested code
17. Benchmarking
Performance Benchmarks
- Status: Not implemented
- Priority: Medium
- Description: Benchmark common operations and training loops
- Benchmarks:
- Operation speed (forward and backward)
- Training loop performance
- Memory usage
- Comparison with other libraries
- Benefits: Track performance, identify bottlenecks
Implementation Status Summary
Completed
- Core autograd system
- Basic neural network layers (Linear, Conv2d, BatchNorm2d, Pooling, Activations)
- SGD and Adam optimizers (SGD needs momentum buffer)
- Basic loss functions (MSE, MAE, BCE, Cross Entropy)
- Sequential container
- Basic tensor operations
In Progress / Needs Work
- SGD momentum buffer (TODO in code)
- Complete backward passes verification
- Broadcasting improvements
- Memory optimizations
Planned (High Priority)
- Additional layers (Conv1d, Conv3d, LayerNorm, GroupNorm, ModuleList, ModuleDict)
- More optimizers (RMSprop, Adagrad, AdamW, AdaDelta)
- Learning rate schedulers
- Additional loss functions (KL Divergence, Hinge, Huber, Focal Loss)
- Model persistence (save/load, checkpoints)
Planned (Medium Priority)
- Activation functions (ELU, SELU, Swish, Mish, Hard Swish)
- Data loading improvements (multi-threading, augmentation)
- Tensor operations (Concatenate, Stack, Split, Gather, Scatter)
- Memory management (pools, profiling, checkpointing)
- Broadcasting (complete NumPy-style)
Planned (Low Priority)
- GPU support (CUDA, OpenCL)
- Advanced features (JIT, parallel backward, double backward)
Contribution Guidelines
When implementing new features:
- Follow existing code style - Match indentation, naming conventions
- Add comprehensive documentation - Doxygen-style comments
- Include unit tests - Test forward and backward passes
- Update relevant documentation - Update docs/TODO_IMPLEMENTATIONS.md
- Add examples if applicable - Show usage in examples/
- Ensure memory safety - Proper allocation and deallocation
- Integrate with autograd - Ensure backward passes work correctly
Priority Justification
High Priority items are:
- Essential for common use cases
- Frequently requested features
- Blocking other improvements
- Core functionality gaps
Medium Priority items are:
- Useful enhancements
- Performance improvements
- Quality of life features
- Nice-to-have improvements
Low Priority items are:
- Advanced use cases
- Long-term goals
- Major infrastructure changes
Notes
- This list is continuously updated as features are implemented
- Priorities may change based on user feedback and requirements
- Some items may be combined or split as implementation progresses
- Consider contributing to high-priority items first
- Check existing implementations for reference patterns